1. Field of the Invention
The invention is generally directed to medical catheters and more specifically to circumstances arising when a catheter which is in place in a patient becomes obstructed.
Catheters are commonplace in the medical field and have a variety of uses. The term "catheter" is commonly used to identify a tubular instrument that is inserted into a body cavity or orifice, naturally or surgically opened. Vascular catheters, for example, come in many different forms and have many different uses. A vascular catheter typically consists of a hub and tubing or cannula through which fluid flows. The hub may include a flash chamber that allows the individual placing the catheter to see blood in the flash chamber that indicates the catheter has entered a vein.
Often, a catheter which has been placed into a blood vessel will become obstructed. There are many ways in which a catheter becomes obstructed. The most common obstruction is typically a blood clot which forms in the lumen of the catheter and clogs the fluid flow through the catheter. These clots often occur in catheters which remain in a patient for an extended period of time. Because of the difficulty inserting such catheters into a patient, it is often desirable to avoid inserting a new catheter into the patient when a catheter becomes obstructed. Consequently, a typical technique in the prior art for dealing with an obstructed catheter is to declot the catheter by adding a declotting agent to the catheter. Typically, this declotting agent will dissolve the blood clot and thereby remove the obstruction from the catheter. The declotting agent may also be a simple saline solution. FIG. 1 shows an example in the prior art of a catheter 10 which has been inserted into the vein 12 of a patient's limb 14. While indwelling in the patient during a period of time, a clot 16 has formed in the catheter 10 thereby obstructing the flow of fluid 18 through the catheter. During normal operation without the clot 16, the catheter 10 conveys the fluid 18 through hub 20 and through the catheter 10 to the distal end 8 of the catheter thereby providing the fluid 18 into the vasculature of the patient. However, when the clot forms the fluid flow becomes obstructed, and this poses a problem for the treatment of the patient.
FIG. 2 shows a typical approach in the prior art to remove the clot 16 by using a declotting solution 26 which is contained within a syringe 22 which has been attached to the hub 20 of the catheter 10. It will be appreciated that this procedure typically involves disconnecting the hub 20 from the fluid feed connection and supply and inserting the syringe 22 into the hub. The declotting solution 26 is introduced into the catheter 10 by applying pressure to the plunger 24 of the syringe 22. One of the dangers of this procedure is the potential high pressures created during the declotting process. A small syringe can easily generate pressures in excess of 100 psi which can rupture the catheter or dislodge the clot downstream into the patient's vasculature. Often, care is taken to try to eliminate this danger by carefully premeasuring the volume of declotting agent to be instilled into the catheter. However, there are inherent uncertainties involved in premeasuring this volume because the clinician has no assurance of the exact location of the clot, and hence the volume of the declotting agent to be used. Too much volume of the declotting agent will often lead to either rupture of the catheter or dislodging of the clot into the patient's vasculature.
Thus, it is desirable to provide a method to prevent overpressurization of a catheter during a declotting process or whenever the potential for overpressurization of a catheter exists.